Telegraph signal regenerator



.um nml ,Il lll R. E. MATHES TELEGRAPH SIGNAL REGENERATOR Filed Dec.`28, 1940 m w En .us5 w. a. ISR .wv kv Smm Oct. 6, 1942.

Patented Oct. 6, 1942 TELEGRAPH SIGNAL nEGENEnA'roB.

` l I Richard E. Mathes, Westileld, N. J., assignor to Radio Corporationof America, a corporation of Delaware 9 Claims.

This invention relates to a telegraph signal regenerator and moreparticularly to an electronic system for regenerating synchronoussignals which may have been deformed in traveling through the conductingmedium from the transmitter to the receiver.

It is an object of my invention to provide a regenerator which is simplein construction, easy to maintain, and which requires a minimum numberof parts.

It is a more speciiic object of my invention to provide a regeneratorwhich eliminates, insofar as possible, mechanical commutation means. andwhich provides dependable regeneration of the received telegraphsignals.

It is a still further object of my invention to provide a regeneratorwhich depends for its operation upon properly timed locally generatedimpulses, these impulses being coordinated with the received signals forcontrolling a so-called locking circuit of more or less conventionaltype.'

I am aware of the fact that other inventors have developed signalregenerative means which are electronic in action and which are suitablefor reshaping telegraph signals. However, in carrying out my invention Ihave found it possible to greatly simplify the circuit arrangementsheretofore known and to provide a simple, rugged and reliable devicewith no moving lparts and the least possible variation in its operatingcharacteristics.

In carrying out my invention I provide means dependent upon the normalrate of reception of the signalling elements for controlling a lowfrequency generator the periodicity of Which is preferably one half thatof the signalling bauds. The

' output of this generator is held in synchronism by means well known inthe art. Such means, for example, may be of the type known and describedin my Patent #2,212,447. In that patent I showed a synchronous correctorapplicable to a receiving distributor for a multiplex telegraph system.Such a corrector may, however, be employed for maintaining .thefrequency and phase of the herein shown baud frequency source so that itwill be synchronized ,withI the mean frequency of reception of themarking signal peaks.

More recent improvements in phase correctors are shown in United StatesPatents 2,258,151 and 2,258,152, both granted to Shenk. Shenk alsoteaches how to maintain an oscillator correctly phased in respect to atrain of incoming telegraph signals with which it is to be synchronized.

Various types of low frequency generators may, of course, be employed.vFor example, it is pos- Appiication December' 28,1940, semi No. 372,112

(ci. 17a-7o) which represents a preferred circuit arrangement sible touse a tuning fork vibrator; or onermay adopt an electronic oscillator incombination with a frequency divider, or any other means for enablingthe oscillator to develop an output to which the baud frequency isharmonically related.

As will be seen from amore detailed description of the invention, theincoming signals to be reshaped are first rectified and then impressedupon one of two control grids of a suitable multielectrode tube forblocking the electronic emission to the anode of this 'tube during thepresence of a marking signal. Another control grid in this tube hasimpressed thereon a periodic zero bias which is sharply peaked by virtueof rectification of the output from the baud frequency source. Thetroughs of the control waves between these peaks maintain a negativebias so as to block the tube completely.

'I'he output from the aforementioned tube is used to control a lockingcircuit which is preferably designed more or less in accordance with theteachings of J. L. Finch, whose U. S. Patent #1,948,103 will illustratesa device of that type.

Other features of the invention will now be explained in more detail,reference being made to the accompanying drawing the sole gure of forcarrying out my invention.

In the drawing I show an amplier l the input side of which is fed fromany suitable radio receiver by which incoming telegraph signals may besensed. These signals are also impressed upon a phase corrector 2 thefunction of which is to maintain a suitable xed phase relation betweenmoments intermediate the front and back edges of the marking signals andthe occurrence of output peaks from the baud frequency source 3.

The amplified signals are fed to a transformer 4 which includes asecondary winding connected between the cathode and the control grid ofa discharge tube 5. The input circuit also includes`v a grounded cathoderesistor 6, and a shunt ca- -former are connected respectively to anodesof a diode rectier tube 9. The secondary of transformer 8 is alsocenter-tapped and connected to the cathode of tube 9 through a cathoderesistor I0. This resistor is shunted by a capacitor Il. The cathode ispreferably grounded.

The rectified and iiltered signal is then applied across resistor I tothe second control grid I2 of a mixer tube I3.

The baud frequency source 3 produces a sine wave which is applied acrosstransformer I4 to tier tube I1 is preferably grounded and is connectedthrough a resistor I8 to a center tap on the secondary of transformerI6.

The output from the rectifier I1 develops sharply peaked voltages acrossthe resistor I8 so that these peaks result in impressing a zero bias onthe iirst control grid I9 of the mixer tube I3. The troughs of the wavedeveloped in resistor I8 produce a negative bias on the grid I9. Thepeaks are periodic and appear equal to the keying speed; that is, thebaud frequency of the received signal.

During signal marking time the current through the rectiiier 9 causesthe second grid I2 to block current to the anode of the mixer tube I3.

`\` IIowever, the sharply peaked pulses from the rectier I1 permittransient currents to pass to the screen 20. It will be seen, therefore,that at times the screen 26 may draw current when the anode of the tubeI3 does not draw appreciabley current. At other times the anode can bemade to draw substantially twice as much current-as the screen by virtueof a zero bias impressed upon the grid I2, while the grid I9 is also atzero bias. The circuits to be controlled under these diiferentconditions will now be described.

The mixer tube I3 has a grounded cathode 2| and an anode 22 which is fedwith a suitable positive potential as indicated by the plus sign of aconductor leading to a junction point between two resistors 23 and 24.Resistor 24 is in the anode circuit, while resistor 23 is in the screengrid circuit.

A locking circuit is shown comprising two discharge tubes 25 and 26.These tubes may be triodes, if desired, or, optionally, tubes of anyother suitabletype. As shown, the cathodes of these 1 tubes 25 and 26are grounded and their grids are negatively biased by virtue of thesource 44 feeding through resistors 45 and 46 to their respective grids.The anodes of the tubes 25 and 26 are fed with a suitable positivepotential with respect to the grounded cathodes, this potential beingapplied through resistors 21 and 28 to the anode of tube 25, alsothrough resistors 29 and 30 to the anode of tube 26. p

A resistor 3I forms a connection between the anode of tube 25 and thecontrol grid of tube 26. Similarly a resistor 32 forms a connectionbetween the anode of tube 26 and the grid of tube 25.

The tubes 25 and 26 operate substantially in accordance withconventional locking vcircuits of which the aforementioned Finch Patent#1,948,103 gives a typical example. The recti- `iied signal applied togrid I2 is merely a conditioner and all action of the mixer tube I3 inits eect on the tubes 25 and 26 is timed by the occurrence of the zerobias peaks on grid I9 which derive from the rectifier I1.

When the tube I3 is blocked by marking signal impressed on grid I2 thepeaks applied to I9 cause the current pulses to iiow in screen grid 24.These pulses cause a momentary voltage drop In resistor 23, which, inturn, is applied through condenser 34 as a negative pulse on the grid oftube 26. 'This causes a diminishing of the plate current, and,therefore, an increase in the plate potential of tube 26. This increasedplate potential is applied to grid of 25 through the voltage divideraction of resistors 32 and 45. This in turn causes an increase in theplate current of tube 25 and a decrease in the plate potential, which,in turn, is applied through the voltage divider action of resistors 3|and 46 to further reduce the grid potential on tube 26.` This action iscontinued until the complete blocking of 26 is obtained by virtue of thelocking bircuit action. Because tube 26 is completely locked, subsequentcurrent pulses through screen, grid 20 of tube I 3 will have no eect solong as the marking condition of the received signal persists.

If at some time between successive zero bias pulses from tube I1 thereceived signal changes from mark to space, then grid I2 will permitthese subsequent pulses to appear as current in anode 22. The amount ofcurrent drawn by screen grid 20 on these subsequent pulses will also bedecreased over the current drawn during the prior pulses. The result ofthis is that although negative pulses are still applied throughcondenser 34 to grid of tube 26 they are more feeble than previously,while, at the same time, negative will cause no current to ow in anode22 but will 75 pulses are applied through condenser 33 to grid of tube25. By virtue of the usual locking circuit action the state will therebybe reversed and will become tube 25 blocking and tube 26 passing.

The relative values of th'e voltages and resistances as used in thelocking circuit arrangement just now described arel so chosen thateither of two stable conditions will be insured such that one tube isalways conductive while the other tube is blocked. In other words, thearrangement for controlling the tubes 25 and 26 is, as the name implies,a. locking circuit arrangement. Whichever one of the resistor pairs21-28 or 29-30 develops th'e greater voltage drop compared with theother, that condition determines which of the two tubes 25 or 26 shallbe rendered conductive while the other is blocked.

An important consideration governing the accuracy of timing of thesquare wave output from the anode circuits of the tubes 25 and 26 isbased upon the cooperative action between the two grids I2 and I9 in themixer tube I3. It should be remembered, therefore, that the grid I9 isintermittently controlled in accordance with a dependable baud frequencysource 3. Abberaticns from the normal times ofthe received signalchanging from marking to spacing impulses and vice versa have no effectupon the timing of the front and back edges of the square wave of outputthe locking circuit.

In order to utilize the square wave D. C. signal which is delivered bythe tubes 25 and 26, I preferably connect a utilization device to pointsintermediate between the resistors l21 and 28, on th'e one hand, andbetween resistors 29 and 30, on the other hand. It will be clearlyunderstood by those skilled in the art that, due to variations in theover-all voltage drop through resistors 21 and 28 in comparison withthat through resistors 29 and 30, th'e terminal 35 will be eitherpositively or negatively biased with respect to terminal 36.

In order to monitor the output from the lockinr circuit by an auxiliarymeans I preferably connect the anode of tube 25 through a voltagedivider 31 to ground. An intermediate tap on the voltage divider 31 isthen connected to a mid-tap on the secondary winding of a transformer.'I'he secondary terminals of this transformer are connected respectivelyto two grids in a duplex triode amplifier tube 39. The anodes of thistube are connected respectively to the terminals of a transformerprimary while the transformer itself is indicated at 40. A mid-tap onthis transformer primary is fed with positive anode potential from thesource 4|, the negative terminal of which is connected to the cathodeofv tube 39.

The transformer 38 is used to impress a tone frequency from any suitablesource 42 on the grids of the tube 39. This tone frequency may be sensedin any monitoring device to which the output leads 43 may be connected.Thus the tone frequency will be applied to the monitoring device duringthe marking signal times, as when the grids of the tube 39 arepositively biased by the marking signals.

Various modications of my invention will suggest themselves to thoseskilled in the art in view of the foregoing disclosure. The scope of theinvention is, therefore, limited only in accordance with th'e claims,

I claim:

1. In a telegraph signal regenerator, a locking circuit for keying themarking impulses of a signal train, a source of oscillations having afrequency to which the baud frequency of the impulses of said signaltrain is harmonically related, a phase corrector responsive to saidimpulses for maintaining a suitable phase relation between the outputpeaks of said oscillation source and the baud centers which aredetermined by said impulses, two rectiers one of which is subject tocontrol by said signal impulses and the other of which is feci withenergy from said source of oscillations, a multi-electrode dischargetube including a cathode, anv anode, rst and second control grids, andscreening electrodes which intervene between the two said control grids,also between the second control grid and the anode, means for causingsharply peaked rectified impulses from said oscillation source to beapplied to the first said control grid thereby to unblock th'e dischargepath in said tube as far as the first screening electrode, meansinterconnecting the signal-controlled rectier with the second controlgrid for unblocking the discharge path in said Atube between thescreening electrodes and the anode during spaces between the markingeleof rectiflers, a multi-grid discharge tube and a locking circuithaving two states of electrical stability for delivering a. square waveoutput signal representing marking and spacing elements of a messagecode, said marking and spacing elements being of baud-unit length andmultiples thereof, the method which comprises adjusting a predeterminedphase of said baud frequency source in accordance with the normalcenters of the marking elements of baud unit length, separatelyrectifying the energy of said marking elements and the energy of saidbaud frequency source, causing a first grid of said discharge ments ofsaid signal train, means for shifting said locking circuit from a rst toa second state of electrical stability in response to the unblocking ofsaid tube only as far as the screening electrodes, and means forshifting said locking circuit` from the second to the first state ofelectrical stability in response to the complete unblocking resistiveand capacitive input circuit connections to said locking circuit wherebyit is caused to be shifted from each state of electrical stability tothe other,

3. In the art of telegraph signal regeneration by means of a local baudfrequency source, a pair tube to be controlled by sharp zero-bias peaksland negative troughs derived from the rectication of energy from saidbaud frequency source, causing a third grid of said discharge tube to befed with a blocking bias potential derived from the rectification ofenergy from said marking elements, causing said third grid to receive azero-bias with respect to the cathode during spacing elements, causing asecond grid to screen the third grid and a fourth grid to screen theanode from electronic emission in said tube, causing one of said statesof electrical stability to be assumed by said locking circuit when asharply peakedv unblocking bias is delivered by the rectified energyfrom said baud frequency source after conditioning the bias on the thirdgrid to a zero value in the presence of a spacing signal, and causingthe other of said states of electrical stability to be assumed when asimilar sharply peaked unblocking bias is delivered from said baudfrequency source after conditioning the bias on the third grid to a.cut-olf value in the presence of a marking signal.

4. A telegraph signal regenerator comprising a rectifier operable inresponse to the impress thereon of marking signal potentials, amultigrid discharge tube adapted to draw anode current in response tothe removal of blocking biases from certain two of itsA grids, means forderiving one of said blocking biases from the action of said rectifier,a sharply peaked baud frequency source for supplying the other of saidblocking biases in the sense that the sharp energy peaks from saidsource produce a zerobias on that one of said grids which is connectedthereto, means for synchronizing saidl source with the baud frequencyofsaid signal potentials, a source of anode and screen grid potentialconnecting the cathode of said tube through resistive elements to theanode of said tube and to certain grids thereof other than those subjectto a blocking bias, a,y locking circuit Ahaving two states of electricalstability, means for producing one of said states in response to theunblocking of said tube so as to draw anode current, and means forproducing the other of said states in response to the partial unblockingof said tube soas to draw screen grid current to the substantialexclusion of anode current.

5. A telegraps signal regenerator according to claim 4 in combinationwith a tone frequency generator for modulating a square wave output fromsaid locking circuit.

6. A signal regenerator comprising a source of telegraph signals, alocal source of alternating, current the frequency of which isproportionate to the baud frequency of said signals, means forcorrecting the phase of said source in accordance with the baud.frequency of said signals, means for 'rectifying said alternatingcurrent and for deriving therefrom pulses of sharp discontinuity, akeying device having two states of stability, and means including adischarge tube of the mixer type having at least four electrodes, ofwhich separate grids are separately controlled by said telegraph signalsand by the sharp peaks of said pulses respectively, for so influencingsaid keying means as to shift the same from one to the other of saidstates of stability in the presence of a marking signal, and in theopposite direction in the presence of a spacing signal.

7. A telegraph signal regenerator comprising a locking circuit havingtwo states of electrical stability, a control device for said lockingcircuit constituted by a discharge tube having a cathode, an anode, afirst control grid, a second control grid and at least twointerconnected screen grids, a source of baud frequency impulses forproducing a blocking bias on said first control grid, said source beingsharply peaked in a direction to minimize the times of application of anunblocking bias to said grid, means for synchronizing said impulses witha mean of baud centers as defined by a received train of markingsignals, means for causing said marking signals to apply a blocking biasto said second control grid, means operative when the first grid aloneis unblocked by said source for causing said tube to draw screen gridcurrent in excess of anode current and thereby to establish one of saidstates of electrical stability in said locking circuit, and meansoperative in the absence of a marking signal and when the unblocking'ofboth control grids enables said tube to draw anode current, forestablishing the other of said states of electrical stability in saidlocking circuit.

8. In a signal regenerator of the type which shifts a keying device fromone to another ot two states of electrical stability, where each shiftis accomplished substantally at one of the norbal baud centers of theincoming signals, a discharge tube for controlling said keying device,said tube having a cathode, an anode, and a plurality of grids includingtwo control grids, means for rectifying energy derived from the incomingsignals, means for applying a blocking bias to one of said control gridsin response to the rectification of a marking signal, a source of baudfrequency oscillations, means for correcting the phase of said source inaccordance with the baud frequency of the incoming signals, means,including a rectifier, for producing a train of sharply peaked impulsesat baud frequency as a derivative from said source, and means formaintaining a cut-ofi bias on the other of said control grids in thepresence of the wave troughs between said sharply peaked impulses,whereby said discharge tube is caused to shift the electrical stabilitystates of said keying device only at the sharp peaks of said impulsetrain.

9. The combination according to claim 8 wherein said discharge tubepossesses a screen grid connected through a resistor to an anodepotential source, and said tube functions in suchV manner that in thepresence of a marking signal electrons are collected predominantly bysaid screen grid, whereas in the presence of a spacing signal electronsare collected predominantly by said anode.

RICHARD E. MATHES.

